Electrochemical Reduction of Carbon Dioxide to Methanol in the Presence of Benzannulated Dihydropyridine Additives

Dihydropyridines (DHPs) have been postulated as active intermediates in the pyridine-mediated electrochemical conversion of CO₂ to methanol; however, the ability of isolated DHPs to facilitate methanol production in a fashion similar to that of their parent aromatic <i>N</i>-heterocycles (ANHs) has not been tested. Here, we use bulk electrolysis to show that 1,2- and 1,4-DHPs (1,2-dihydro­phenanthridine and 9,10-dihydro­acridine) can mediate the substoichiometric electrochemical reduction of CO₂ to methanol and formate with Faradaic efficiencies similar to those of the corresponding ANHs at Pt electrodes. 1,2-Dihydro­phenanthridine furthermore exhibits improved CO₂ reduction activity compared to its parent ANH (phenanthridine) at glassy carbon electrodes. These results provide the first experimental evidence for the participation of DHPs as additives in electrochemical CO₂ reduction